The present invention relates generally to a sheet storage case for storing therein a stack of sheets. More particularly, the invention relates to a sheet storage case adapted to be assembled into a sheet feeding device which feeds out an uppermost sheet of the stack of sheets.
Various types of sheet storage cases or sheet cassette cases have been known in the art. One of the conventional sheet storage cases includes a plate-like member provided within a cassette case which regulates a stacking position of the sheets. The position where such a plate-like member is provided agrees with the size of the sheet to be received. With this structure, no gap is provided between the sheets and the sheet position regulating member. Consequently, it would be rather difficult to dispose a stack of sheets into the cassette case, particularly, to align the edges of the stack of sheets with one another.
In another conventional sheet cassette case, a snubber is provided therein which is assembled in a sheet feed means provided in a copying machine, which sheet feed means takes out each sheet. In such sheet cassette case, an uppermost sheet of the stack of sheets is taken out by the action of the sheet feed means of the copying machine. In this case, one edge of the sheet is temporarily engaged with the snubber so that the sheet is bent. Accordingly, subsequent sheet is separated from the uppermost sheet because of it inherent rigidity. However, a sheet portion engaging the snubber may be subjected to scratching or damage. Particularly, in case of a particular type of the sheet such as the developer sheet, developer materials coated on the surface thereof may be scraped off due to the frictional engagement with the snubber. Therefore, a desirable image formation on the sheet may not be attainable.
A sheet cassette for use in a copying machine is one of the typical examples of the sheet storage case. In such a sheet cassette, a guide plate is fixed in a sheet case by screws, etc. for regulating a position of the sheets. However, it would be rather troublesome in storing the sheets therein, and if a plurality of sheets are irregularly stored in the cassette, the sheets may be deformed or folded.
An image recording apparatus which employs a photosensitive pressure-sensitive recording medium has been known in which special attention should be made with respect to a moisture absorption into the recording medium. In the conventional apparatus, the photosensitive pressure-sensitive recording medium exposed to light in accordance with an imaging information is superposed with a developer sheet (developer material coated sheet) and are uniformly pressed together. In this case, if irregular pressure distribution is provided with respect to the every pressing positions, wrinkles may be generated in the developer sheet or the photosensitive pressure sensitive sheet. The wrinkles are considered to be produced by non-uniformity in density of a base sheet which constitutes the developer sheet, which nonuniformity may be caused by moisture absorption from cutting edges of the developer sheets.
The developer sheets undergo excessive moisture absorption thereinto through an upper surface area of the uppermost sheet and through cutting edges of the sheet stack. For example, when leaving the developer sheet at an atmosphere having a temperature of 28.degree. C., and humidity of 90% for about 30 minutes, a large amount of moisture is absorbed into the sheet. If image recording operation is carried out with employing such developer sheet having large water content, the uppermost sheet does not provide significant problem, since water is uniformly absorbed in an entire area thereof. However, with respect to the subsequent sheets, since water is absorbed into the sheet through the cutting edges, the edge portions of the sheet provide high moisture content ratio, whereas a central portion of the identical sheet still has its dried state. As a result, irregularities in density is provided in the sheet, to thereby promote generation of the sheet wrinkles.
However, no special attention has been drawn to the conventional developer sheet cassette in respect of the moisture absorption. Therefore, an operator must store only a required amount of sheets into the cassette for the copying, and such sheet number counting works may be troublesome for the operator.
In still another conventional sheet storage container, a bottom plate is provided for mounting thereon cut sheets etc. The bottom plate merely serve to mount thereon the sheets. However, in case of exchanging the sheets with another kind of the sheets, a finger must be inserted into a narrow space within the container body for taking out the sheets, which has been troublesome.
In a conventional image recording apparatus of the type having a sheet feeding device, there are provided two sensors, one being adapted for detecting a sheet feed cassette assembled into a main body of the apparatus and the other being adapted for detecting sheets within the cassette. However, employment of the two sensors is disadvantageous in terms of cost and an operational reliability. Further, installations of the mechanical components and assembling works may be troublesome. Furthermore, it would be difficult to perform detection of the sheets within the cassette by a simple arrangement.